The Effect Of Rolling And Heat Treatment Of AZ31 Magnesium Alloy Sheet On Its Deep Drawing Performance

Magnesium alloys as the lightest metal structure material which can be used in engineering,have many advantages such as high specific strength,specific stiffness,excellent cutting property,excellent thermal conductivity,electromagnetic shielding and good environmental compatibility.Therefore,magnesium alloys have broad application prospects in automotive,communications,electronics and other fields.The application of stamping and deep drawing technology can not only make full use of magnesium sheet excellent performance for thin and lightweight products,but also greatly improve production efficiency and product qualified rate.So the research and development of forming technology for magnesium alloy sheet has been a hotspot in recent years.But magnesium alloy has a typical hexagonal close-packed(hcp)crystal structure with limited number of operative slip systems at room temperature,which lead to has low plasticity at room temperature.And during the heat forming process at high temperature,components are over oxidized.Therefore,it is of great significance to improve the warm forming properties of magnesium alloy sheets by using different rolling and heat treatment processes.In this research,firstly,the extruded of 1.4 mm thickness AZ31 magnesium alloy sheets are warm rolled to 0.5 mm sheets by a six-roll mill with seven different rolling routes.Through the microstructure observation and tensile tests at room and high temperature of 0.5 mm thickness rolled sheets,the microstructure evolution,the tensile,deep drawing performance index including plastic strain ratio,strain hardening index and yield strength ratio etc.are obtained.Through analysis and comparison,the reasons influencing the deep drawing forming properties of the rolled AZ31 magnesium alloy sheet are revealed.Secondly,10 groups of heat treatment experiments are carried out,and the same tests are repeated for the 0.5 mm heat-treated AZ31 magnesium alloy sheet,in order to explore the optimum heat treatment process for the stamping and drawing process.Finally,The deep drawing experiments of AZ31 magnesium alloy sheets after rolling and heat treatment are carried out at room temperature and high temperature to analyze the effect of rolling method and heat treatments on the deep drawing performance.The results of the study are as follows:Firstly,comparing with symmetric rolling,cross-asymmetric rolling can effectively break grains with different orientations and obtain uniformed grain size,and the(0002)texture is about 10° tilt with normal direction.This microstructure can not only improve the rolling ability but also can improve mechanical properties,anisotropy and deep drawing forming properties of AZ31 magnesium alloy sheet by redistribution of the shear stress in roll bite zone.With the increase of cross rolling reduction rate,the effect is more obvious.When the cross rolling reduction rate reaches 50%,the microstructure is optimal,the anisotropy is the smallest,the mechanical properties are the best,the deep forming performance is the best,and all the indexes are better than the other cross rolling reduction of the AZ31 magnesium alloy sheet,which has already shown its excellent plastic forming properties.Secondly,it is found that small recrystallized grains and random texture can be obtained at 400℃ for 10 minutes heat treatment.The AZ31 magnesium alloy sheet with such heat treatment condition,which is time saving and high efficiency,has good mechanical properties and forming performance.Finally,in the stamping drawing experiment,it is found that the drawing deformation temperature,heat treatment conditions and rolling method play an important role in the deep drawing of AZ31 magnesium alloy sheet.After the magnesium alloy sheet with a cross rolling reduction ratio of 50% is subjected to a heat treatment at 400℃ for 10 min,the AZ31 magnesium alloy sheet can successfully prepare a deep drawn 9 mm sample at room temperature.